Multiunit, single scale oximeter



July l5, 1947. B. sMALLER MULTI-UNIT, SINGLE SCALE OXIMETER Filed Oct.25, 1945 2 Sheetsfsheet l FIGA PER CENT SHTURQTION' ERE .SETTING ERR wmim M m .wf 4I u e l 4 N M 5 -I W www July 15, 1947. B. sMALLl-:R

MULTI-UNIT, SINGLE SCALE OXIMETER 2 Sheets-Sheet 2 Filed Oct. 25, 1943FIGA- Z f 5, f w www@ w IY 7 i, 02, 9. 2 j M @a K/mv 5. m ,d F WV/2M, M@7 W2 ym WW (f8, MW f v4 N v. ma 5 Patented July 15, 1947 UNITED STATESPATENT DFFICE MULTIUNIT, SINGLE SCALE OXIMETER Bernard Smaller, Chicago,Ill.

A Application October 25, 1943, Serial'No. 507,634

(Granted under the act of March 3, 1883,'as amended April 30, 1928; 370O.l G. 757) 4 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to oximeters and its general object is to providea multi-unit, single scale oximeter.

The known prior art consists oi an oXimeter whichmak-es u-se of theldifference in light transmission properties of a green and la redfilter to measure the percentage of oxyhemoglobin in the blood. Inpractice the subjects ear is clamped by an earpiece which includes asource of light on one side of the ear and two photocells on the otherside, one photocell being covered by the green lter and producing acurrent which depends on the total blood thickness of the ear, the otherphotocell being covered by the red lter and producing a currentdependent on the amount of oxyhemoglobin in the blood. The band of lightfrequencies passing through the green lter is absorbed almost equallywell by both oxyhemoglobin and reduced hemoglobin, while that passingthrough the red lter is more strongly absorbed .by reduced hemoglobin;hence by measuring the amount of light falling upon the photocells, onemay measure both the-blood thickness and the oxygenated blood. Aninstrument (essentially a galvanometer) can be calibnated in terms ofper cent saturation of oxyhemoglobin and by means of enlargedilluminated scales very sensitive readings of the condition of thesubjects blood may -be taken at any point desired..

To those skilled in anesthesia land oxygen therapy, the value of thedescribed apparatus will be obvious. In altitude chambers, used by theArmy Air Forces, and in decompression chambers, employed by the Navy inconnection with deep sea diving, the described oximeter will be usefulsince it permits readings to be taken continually from outside thechamber of the condition of the subjects blood, thereby making itpossible to guard against acute anoxemia or even collapse.

The speciiic objects of this invention are to provide an oximeter havingthe following advantages: Y

First, the ear type and per cent saturation readings are taken with thesame light intensity, which is so low that no discomfort is caused.

Second, the ear is kept in thermal equilibrium so that there ispractically no drift.

Third, the multi-scale is replaced by a single scale. By utilizing thissinglescale a number of ear units can be wiredv into the same circuit.

Fourth, a single photocell switch is employed to control al1 the earunits.A s

Fifth, the compensation for the ear type also compensates forvasodilation, and the instrument will always give a trueL reading nomatter how muchvasodilation occurs.

In the accompanying drawings forming a part of this specification, Y

Fig, 1 is a simplified wiring diagram, being one-sixth of a completediagramfor the actual oxiineter,y minus the earpiece circuits; Y

Fig. 2 is an elevation ofthe single scale of the ofximeter;

Fig. 3 is a. diagram of an earpiece shown with part of an ear insection;

Fig. 4v i-s la schematic lwiring diagram of the iilter or ear typecircuit;

Fig. 5 is |a schematic wiring diagram of the suppression circuit; and

Fig. 6 is a schematic wiring diagram of per cent saturation circuit.

Referring particularly to the drawings, an earpiece of the prior arthaving ear clamping means (not shown) is provided with fa 6 v.-lampbulbI2, photocells I3,l I4 which are shielded from each other, greeni-llterI5 and red lter I6, and is adapted to be secured to the scapha membraneof the ear II of a subject or patient. Instead of the ear, other partsof the body could be clamped. Conductors I8, I9 connect lamp bulb I2with a 6 v. circuit, conductors 20, 2I connect the green filteredphotocellv I3 with a selector switch (to be described)v `and'conductors22, 2| Aconnect the red filtered photocell I4 with the same selectorswitch. The bulb I2 is energized from a source of 6 v. current such as abattery 23 when the main switch 24 is closed. Conductor I9 connect-swith a variable or iilter rheostat 25 having alead 26 connecting it witha switch 24, while conductor I8 is directly connected rto switch 24 asshown. The movable contact 25a of the lter rheostat provides means forcontrolling the intensity of the light emanating from bulb I2.

Topcontrol the various earpiece circuits, a 6 pole, 6 position gangselectory switch 2l is employed, with connections forl plugging in sixear unit ',extensions, whereby six subjects may undergo a test together.A photocell switch 28 is coupledby leads 29, 3B, 3|, 32, 33 and 34 tothe selector switch and further has a lead 35 and shunt 36 connecting it,to lead 26whereby the source of `current; is coupled with the photocellswitch;Y Moreover there is a galvanometer switch 3l coupled by leads 38,39 with the selector switch, and also -with thephotocell switch. Thegalthe vanometer switch may couple a table galvanometer 40 in thecircuit by leads 4I, 42 (with a re-V sistance 43 shunted across leads 38and 42) or may couple a projection galvanometer (not shown) by means ofleads 45, 46. The projection galvanometer is provided With a preferablyilluminated scale `'41, .but the `:scale light and'its-circuit areomitted because they' do not contribute to an understanding of theinvention.

A rheostat 48 for controlling the ear setting is shown coupled throughresi-stance 49 with `a lead 50 connected to light switch'2`4. 'The thrside of rheostat 48 is connected to lea-"'d F3=5'fso as to be inparallel with the filter rheostat 25. The movable contact I of'rheosta'tl "'i's'co'nnected to the selector switch by means oflead 52.Rheostat 48 makes it possible to `put a variable ,potential acrosseither galvanometer, toig'ivfe ;a .galvanometer current of onedirectionwh'e'n' the photocell switch is set to the ear setting positionand lof the opposite direction Vwhen the photocell switch is in the percent 'saturation' Afposition. n'th'is way the operator-can, intellect,set back th-efz'eoiof the galyanometerl'when no `current isvflowingfrfciin Lti-iereclllterelphotocell) To provide asensitivity--cntrolin -thephoto'cell circuitan Ayrton's'hxint5'3-1'is4'c" ctedfby leads 54 and 55 to the selectorswitch,-lead55{beingicon- 4nec'ted withthe movable -cntcto'the Ayrtonish-lint. Ayrton s'hu'n't uis a circuit 4utilized where one desires i axed iScr-itic'al `dampi-ngresistance #in parallel with t"thelgalvanoineter and yet a variablefsensitivity of the galva'norrieter.The third -lead A"51-i`s connected `--througfli conductor 2| with theselectors tch. Now'wh'enthe l-pliotocell' switch is setftolthe ff-lter"position,` the full sensitivity of the Flgali'fantiin'feter A-is:connected to the green'lteldphtoll Y1(-lac'iszil 2and 2l) Yandwhen itis set to per c @turnier-'imposition, `the 're'd filtered fph'o't'ocelllis `connected through leads 2| and-522th 'tlievariables'hunt'of 'thegalvano'meter. 'Thiis'the-Zerocan be'se'teback byn-'ieanstof-lthevariablepotntialto' any value 'as yshown 'by the "lterf read-in'gf andthe "sensitivity controFoPtle Ayrton s'llunt'l can b'e vv'iva'nced yt0any value desired. 'The e'a'r settings for the various i ear'thicknesses-are "'s'uchfthat the prior-artis mmtnsc'ale forfd-iirerentear'thicknesse's may be replaced by'rth'e single scale"-41'1upon using the proper ears'etting. 'Iihe'` sensitivitycontr'oliife. Ayrton'shu'nt) '#can -then=be advanced 'until the movable'light fb'ea'm iofithe projection gah/anometer shows 100% saturationTontlfle scale' 41 -ifA the subject isibreathing'oxygenzor` 95% ifbreathing :atmosphericain In Lthefdiagrarn'fof A1on1-y iive "leads #are:shown i'for one Aear 'whereas in the prefer-red apparatus six'setsofthese leads :are used for ythe -six eazfunitslemployed.Furthermore,-.there will ybe `-'six Vsets 'of` rheostats `25, 48 fana53, but only fone selector.swi'tchf-` o'n'e qoliotocelliswitch, onegalvancmeterswitch-fandveone scale, when :six subjects are to be tested.fTh'e' current'maybesupipliedby'the single'fbatterylS and controlle'd'byvthe single switch- 24forfall sixfisetswby-eonnecting Howeveryit willbe-cleartnat'fmore 'than six subjects may vfbefteste'cl yifappropriate'fchanges in the tdescribedriapparatus -Vare made. I

'The selector switch "-21 'hasfxedcontactsG-l, T12, an"f63,to whichtheteifn'i'inals'of leads '2.0, .22, kland i2 I `irespe'c'I";ively,` areconnected; 'and -con- Ftacts B'LIf'fES, fand -fto which Jthe 'terminalsof yle'aiisSZ,'54, fand 55,- respectively,` .are connected. Five 'othergroups offsix 'xedlcontacts 61,158,169

and 88, 89, 90; 10, 1I, 12 and 9|, 92, 93; 13, 14, 15 and 94, 95, 96;1E, 11, 18 and 91, 98, 99; and 19, 80, 8| and |00, IOI, |02 arerespectively adapted to be connected to five other ear units each unitincluding a rheostat as 48 and an Ayrton shunt as 53 in the manner shownfor connecting the ear unit'tothe contacts il-iiiic'lusiva'to provide avsix position selector switch. The selector switch is turnable manuallyto any one of the six posilitions, each position closing a circuitthrough one of the six groups of contacts identied above. The movableparts of the selector switch 21 are difagrammatically indicated by thearrows 82, 83,

, 84, 85, 86, and 81 which represent movable con- "tactsoperative'as agang and are in two groups,

.conta'ctsf 86, and 81 being adapted to cooperate with the xed contactsto close a circuit in any `one of-'the six `positions to electricallyconnect leads 28, '22,` and 2| of the corresponding ear unit with theleads 32, 33, and 34. The other group 'of rnovable contacts '4182, 183,and 84 are adapted to cooperate '-with the corresponding xed contact'stoVclose ya circu'iti'n rariyfo'ne .of the six positions to electricallyconnect .leads 52, 54, and 55 of the corresponding ear unit with theleads T29, 'ftilfand'537|'.V Referring-toene ear unit circuit as shownin Fig. 1 it will be seen that when 'the switch 24 i is closed the`circuit `to-th'e light source I'Eis-close'd as "will'lce .apparentand4light will shine Itlfirou'gh the ea'r vii'ien'i-bran'e .I V1, reachingfthe pho it'oc'ells -I4 throngfh'the iilters |15, IB, respectively. Theselector Vswitch 21'is .now operated te 'connect the :ear Eunit :shown-in Figs. l and 3 'with *the phot'ocell lswitcl'i and the galvanometercircuit, :and v"also *to 'cou-ple the potentiometer 'd8 `and resistorf531into said galyanometer circuit.

The photocel'lfswi'tch' is coup'led to the selector switch as.alreadyf'm'entioned and has four positions, viz.,"an"offfposition `withdeadV contacts'll,1 I.`Il0, I.I4.;ian ear setting position, withcontacts 1205, |139, and :I .'I 3; a filter position,-with contacts 104,|108, and I I2; and a per cent saturation'position, withcontacts |03,|01, 'and III. All these .contacts Tof Vthe .photocell s'witch are' xedAcontacts,"a'gainst which'the rmovable contactsv "I I8, I'I."9, I2IIIclose. vLike .contacts |06, 'H0 and H4, Lthe contacts YH011,2I08'1a'ndI'09 are'dead. Here -a'gain'the moi/'table contacts of theswitch Vare @show/n ldiagrammatically as arrows, lextending Ifromterminals I I5, '.II'B, 'II1 which are coupled 'respectively to leads34, -3'I, and 39. Lead v9 is connected .tofcon'tacts |103 and II'3`whilelead 35 is-connected ytoc'ontacts |05, lI I I.

The g'a'lvanometer Iswitch '31'receives cur-rent A.through .leads '33and 39,1:and permits `the operator :to connect'rei'therthe' tablegalvanorneter 40 or a :projection fgalvanometer (not shown) lto theinpu't circuit. vTlriewwfiring of switch 31 is such that when vonegalvanometer is connected, Vthe other is's'horted-'acrossitsfterrninals-to prevent excessive :swinging fof the'suspension l'with possible damage. .Resistorvil'xincombination withresistor'53, func- ;tions .simply as fa critical damping resistance toinsure the best operating characteristics of the fgalvanometer.

With .this i'description of the 'apparatus andthe manner in which itsparts are connected, the 'operation will now='bedescribed, reference`being made'to Eigs'. .4e-6, tas'tl/iesediag-rains arermuch easiert'ozfo'llo'wl'i'.'li'a'nil'ig.v l,

To operate theoximeter, the galvanometer light is rst turned on,Vv and4the phot'ocell 'switch 28 is :turned'rto oi`fpesition.x 'Then thegalvanometer .iis adjusted Lto Vrea'dt5l'l pn :scaler 41,iwhichlprovides a zero .setting 'or basing ip'oint. To effect'this ad;

justment,y the scale itself lmay be moved longitudinally in eitherdirection. Then Alight switch 241s closed and the desired number of earunits arerplugged into the extensions of the selector switch.. Thenthere is a pause of several minutes toallow the photocells to come tothermal equilibrium. Now the photocell switch is closed to the filterposition (Fig. 1) wherein the filter or ear type circuit of Fig. 4 isclosed.

. The galvanometer is now connected solely to the greenltered photocellI3 as a source of current, ,and the current iiows as indicated by thearrowsin Fig. kfl. Before using the apparatus to determine the per centsaturation of oxygen in the blood of the subject, the output of thegreen filtered photocell is rst standardized. (This is necessary becausephotocells as now made have diierentA sensitivities.) Thisstandardization is accomplished by simply inserting a neutral filterinstead of theear I1 between the lamp I2 and the photocells and thenadjusting the intensity of the light by means of variable resistor 25,25a until the photocell output current causes the galvanometer beam toreach the lter graduation on theupper scale of Fig. 2. This procedure isrepeated for each subject, whenever several subjects are underobservation simultaneously, since the photocells of each ear unit willprobably differ from those on all the other ear units. The neutral lteris now replaced by the ear, whereupon the galvanometer beam will bedeflected to a numerical value corresponding approximately or ex actlyto one of the graduations under the legend ear type, on the bottom scaleof Fig. 2. This deflection is a measure of the ear thickness or bloodthickness of the ear under observation.

. Having noted the reading on the "ear, type scale,'the operator willclosethe photocell switch 28 tothe ear setting position (Fig. 1) whichputs in operation a suppressioncircuit as input to the galvanometer. The`suppression circuit is energized from the battery 23 and its principalleads are leads 50 and 35. See Fig. 5, showing the direction of currentflow. Potentiometer 48 operates as a Variable potential divider,allowing a variable amount of current to flow into the galdened as theposition of the galvanometer beam `or needle when no photocell currentis owing through it.) This adjustment or suppression of the galvanometeris accomplished electrically by the suppression circuit of Fig, 5, whichmoves the galvanometer beam or needle to the left of the scale, Fig. 2,i. e., contra to the normal direction. However, in order to observe theamount of suppression current to be applied, in this position ofthephotocell switch the direction of the suppression current is reverseand the galvanometer gives a reading to the right on the scale where itcan lbe seen-and measured. By means of potentiometer 48 the amount ofthe suppression current is varied until the galvanometer` reads on theear setting scale of Fig. 2 the numerical value that was observed whenthe ear type reading was taken. y,Where several subjects are observedthe above operationshould be made for every subject underobservation. Y

The photocell switch is now set to the per cent 6 saturation position,and there are then two ine dependent sources of current on thegalvanometer circuit. If the red filtered photocell I4 were notgenerating any current, the suppression circuit would tend to drive thegalvanometer beamer needle to the leftL on the scale. (In'Fig. 6 thesuppression input leads have been reversed for` simplicity.) Thus whenno photocell current flows, the galvanometer zero has been suppressed adeterminate amount and single scale operation is made possible. Now thered filtered photocell i4 generates a current whose strength isproportional to the relative amounts of oxyhemoglobin and reducedhemoglobin present in the blood of the ear. The percentage of thisgenerated current that will flow through the galvanometer is determinedby potentiometer 53 which operates now as an Ayrton shunt. The currentflow due to the current generated by photocell I4 is indicated by thearrows in Fig. 6, and the strength of said current owing through thegalvanometer is determined by potentiometer 53, 56. This potentiometeris adjusted by the operator so that the galvanometer reads (i. e., 95%saturation) on the upper or per cent saturation scale, Fig. 2, thisbeing a fixed known point of saturation for a normal subject breathingroom air at approximately sea level. (If the subject is breathing pureoxygen, the galvanometer should be brought to read on the same scale.)Subsequent readings of the galvanometer should now give the correctvalue of arterial saturation in per cent, on the upper scale of thegalvanometer (Fig. 2). It will be noted that the current supplied by thephotocell I4 was required to bring the galvanometer reading from asuppressed zero position to the left of the scale. Thusthe true lengthof the per cent saturation scaley 41 is dependent on the ear setting andhence ear type. This electrical expansion or contraction of scale 41 toaccommodate various ear types allows for single scale operation and isone of the features of the invention.

The final scale reading is not the same in all cases, nor is it the samewith one subject, if he is subjected to an altitude chamber test, forexample. As his blood stream loses oxygen, the light beam on thegalvanometer scale drops from 100% (if breathing oxygen) or 95% (ifbreathing air) down to 90, then 85, then 80, and so on. The test isnearly always stopped before the subject loses consciousness, and thereading on the galvanometer scale outside of the test chamber will givea clear warning when to expect the subject to become faint prior tolosing consciousness.

After thermal equilibrium is reached and the altitude run under way, theper cent saturation of each of six subjects may be obtained separatelyby rotating the selector switch. If vasodilation of the ear is suspectedduring the course of a run (i. e., the per cent saturation reading istoo low for the corresponding altitude) ,A check the ear setting readingby adjusting the photocell switch Vto the ear setting position and if achange has 4tered photocell(Y and a red filtered photocell, saidvanometer will, when applied to the galvanometer with reversed polarity,reduce the deection produced by the red ltered photocell by an amountproportional to the ear thickness corresponding to said one graduationof said second set, means for applying to the galvanometer a voltageindependent of the voltage applied by said photocells, manuallyadjustable means for varying said independent voltage so as to deflectthe galvanometer to the ear type potential indicating graduationcorresponding to the thickness of the subjects ear, said means forselectively connecting the photocells, to the galvanometer includingmeans for reversing the polarity of said independent voltagesimultaneously with the connection of the red filtered photocell to thegalvanometer, and manually adjustable means for varying the voltageapplied to the galvanometer by said red ltered photocell to deflect thegalvanometer to a point on the concentration scale representative of thenormal oxygen concentration for the atmosphere available, wherebysubsequent changes in oxygen concentration of the blood will beindicated directly on the concentration scale.

BERNARD SMALLER.

REFERENCES CITED UNITED STATES PATENTS Name Date Millkan Sept. 26, 1944Number

